In a conventional exposure apparatus employing a step-and-focus method, a predetermined exposure process is performed while a wafer subjected to exposure is brought to a stationary state. Therefore, by compensating, prior to the exposure process, for distortion components generated when a mask image is transferred onto the wafer, distortion generation can be prevented. For instance, Japanese Patent Application Laid-Open No. 01-039726 discloses a method of compensating for a distortion by a characteristic of a lens used in exposure processing. Furthermore, Japanese Patent Application Laid-Open No. 06-349703 discloses a method of monitoring heat generated by exposure or temperature variation in an environment at the time of exposure, and feeding the monitored results back to an exposure apparatus. Both of these methods take effects by performing distortion compensation immediately before an exposure process employing a step-and-focus method.
In the above-described exposure apparatus employing the step-and-focus method, since exposure is performed on one substrate, distortion compensation before exposure is possible, and the compensation effect is reflected on the substrate. On the contrary, in an exposure apparatus employing a step-and-scan method (scanning exposure apparatus), since an exposure area on the substrate changes with time, even if distortion compensation is performed prior to exposure as in the step-and-focus exposure apparatus, the compensation effect cannot be reflected on each exposure area. Note, in the following description with respect to a scanning exposure apparatus, a positional error (distortion in one shot) between a designed reticle image and a transferred image on a substrate in each shot, as well as a distortion of a background pattern caused by multiple exposure will be referred to as a “distortion.”
Factors that disturb effectiveness of distortion compensation in the scanning exposure apparatus include a production error in a projection lens, uneven driving thrust of a reticle stage and a substrate stage, an influence of vibrations, and so forth. These are distortion generation factors unique to a scanning exposure apparatus.
In a case of driving unevenness of a reticle stage and a substrate stage at the time of scanning, exposure light is caused to be deflected by a bow of the stages, and the unevenness can be compensated for by measuring an influence of the bow of each stage and storing the data in advance. However, in a case wherein the unevenness is caused by uneven thrust of a stage-driving motor or vibrations of a mechanical system, the pattern of each distortion generation cannot be determined in detail unless the actuator is driven to perform actual scanning exposure.
Furthermore, in actually performing the scanning exposure, even if control parameters are compensated for at each position corresponding to the scanning exposure, an influence of distortion cannot be removed in many cases because the aforementioned factors conspire to influence the distortion in various ways. Therefore, conventionally, the compensation value for calculating a driving value is determined based on an empirical intuition of an operator of the exposure apparatus.